Hit:1 http://ppa.launchpad.net/kritalime/ppa/ubuntu focal InRelease
Hit:2 https://brave-browser-apt-release.s3.brave.com stable InRelease
Get:3 https://brave-browser-apt-release.s3.brave.com focal InRelease [2,820 B]
Get:4 http://repository.spotify.com stable InRelease [3,316 B]
Get:5 http://ppa.launchpad.net/system76/pop/ubuntu focal InRelease [18.0 kB]
Hit:6 http://us.archive.ubuntu.com/ubuntu focal InRelease
Get:7 http://us.archive.ubuntu.com/ubuntu focal-security InRelease [107 kB]
Err:3 https://brave-browser-apt-release.s3.brave.com focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4FE13824E3FFC656
Hit:8 http://apt.pop-os.org/proprietary focal InRelease
Get:9 http://repository.spotify.com stable/non-free amd64 Packages [1,644 B]
Get:10 http://repository.spotify.com stable/non-free i386 Packages [1,171 B]
Get:11 http://ppa.launchpad.net/system76/pop/ubuntu focal/main Sources [25.5 kB]
Get:12 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease [107 kB]
Get:13 http://ppa.launchpad.net/system76/pop/ubuntu focal/main i386 Packages [26.8 kB]
Get:14 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease [98.3 kB]
Get:15 http://ppa.launchpad.net/system76/pop/ubuntu focal/main amd64 Packages [52.9 kB]
Get:16 http://ppa.launchpad.net/system76/pop/ubuntu focal/main Translation-en [20.1 kB]
Reading package lists... Done
W: GPG error: https://brave-browser-apt-release.s3.brave.com focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4FE13824E3FFC656
E: The repository 'https://brave-browser-apt-release.s3.brave.com focal InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.